public class LinkedList implements IList{
    static class ListNode {
        public int val;
        public ListNode next;
        public ListNode prev;

        public ListNode(int val) {
            this.val = val;
        }
    }

    public ListNode head;
    public ListNode last;

    @Override
    public void addFirst(int data) {
        ListNode node = new ListNode(data);
        if(head == null) {
            head = node;
            last = node;
        }else {
            node.next = head;
            head.prev = node;
            head = node;
        }
    }

    @Override
    public void addLast(int data) {
        ListNode node = new ListNode(data);
        if(head == null) {
            head = node;
            last = node;
        }else {
            last.next = node;
            node.prev = last;
            last = node;
        }
    }

    @Override
    public boolean addIndex(int index, int data) {
        ListNode node = new ListNode(data);
        ListNode cur = head;
        if(head == null){
            return false;
        }
        if(index == 0){
            addFirst(data);
        }
        if(index == size()){
            addLast(data);
        }
        while(index != 0){
            cur = cur.next;
            index--;
        }
        node.next = cur;
        cur.prev.next = node;
        node.prev = cur.prev;
        cur.prev = node;
        return false;
    }

    @Override
    public boolean contains(int key) {
        if(head == null){
            return false;
        }
        ListNode cur = head;
        while(cur.next != null){
            if(cur.val == key){
                return true;
            }
            cur = cur.next;
        }
        return false;
    }

    @Override
    public void remove(int key) {
        if(head == null){
            return ;
        }
        if(head.val == key){
            head = head.next;
        }
        ListNode cur = head;
        while(cur.next != null){
            if(cur.val == key){
                break;
            }
            cur = cur.next;
        }
        if(cur != null){
            if(cur.next == null){
                last = last.prev;
                last.next = null;
            }
            else {
                cur.prev.next = cur.next;
                cur.next.prev = cur.prev;
            }
        }
    }

    @Override
    public void removeAllKey(int key) {
        ListNode cur = head;
        while (cur.next != null){
            if(cur.val == key){
                if(cur == head){
                    head =head.next;
                    head.prev = null;
                }
                else{
                    if(cur.next == null){
                        last = last.prev;
                        last.next = null;
                    }else {
                        cur.prev.next = cur.next;
                        cur.next.prev = cur.prev;
                    }
                }
            }
            cur = cur.next;
        }
    }

    @Override
    public int size() {
        if(head == null){
            return 0;
        }
        ListNode cur = head;
        int len=0;
        while(cur != null){
            cur = cur.next;
            len++;
        }
        return len;
    }

    @Override
    public void display() {
        if(head == null){
            return ;
        }
        ListNode cur = head;
        while(cur != null){
            System.out.println(cur.val+" ");
            cur = cur.next;
        }
        System.out.println();
    }

    @Override
    public void clear() {
        head = null;
        last = null;
    }
}